Certain types of essential oils are known to be environmentally friendly and effective in providing a variety of benefits. The use of such oils in many commercial applications, however, has been limited due to their high volatility and instability in the presence of oxygen. Attempts to overcome this problem often involve the use of larger amounts of essential oils to prolong desired results. Unfortunately, this just leads to another problem in that simply incorporating higher concentrations of essential oils can lead to unintended and sometimes damaging results. Other attempts have involved the encapsulation of the oil component with certain types of polymers, such as proteins, in the presence of a solvent. For example, an article entitled “Encapsulation of Essential Oils in Zein Nanospherical Particles” (Parris, et al., J. Agric. Food Chem. 2005, 53, 4788-4792) broadly describes the encapsulation of thymol in zein nanospheres by mixing the oil with zein particles in the presence of a solvent (e.g., ethanol). The particles are said to be useful for oral or injectable administration of biological materials into the body. Another article entitled “Controlled Release of Thymol from Zein Based Film” (Mastromatteo, et al., J. Innovative Food and Emerging Technologies 2009, 10, 222-227) broadly describes films formed by dissolving corn zein and glycerol into ethanol, and thereafter adding thymol to form a solution. The solution is poured into a Petri dish and dried to form the film.
One problem with the techniques described above is that they generally rely on solvents (e.g., ethanol) to help dissolve the essential oil into a solution. A disadvantage of the use of solvents is that it puts a limit on what type of components may be employed in the composition. Additionally, solvent-based solutions require a substantial amount of time, energy, and materials for processing. Moreover, a portion of the essential oil may escape from the solution when the solvent is evaporated, which requires the use of a greater amount of oil than would normally be needed. Notwithstanding the above, the ability to use a “solventless” process in an oil and protein combination is complicated by the tendency of proteins to lose their flow properties when exposed to the intense shear and elevated temperature normally associated with melt processing. For example, proteins may undergo a conformational change (“denaturation”) that causes disulfide bonds in the polypeptide to dissociate into sulfhydryl groups or thiyl radicals. Sulfhydryl groups form when disulfide bonds are chemically reduced. Thiyl radicals form when there is a mechanical scission of disulfide bonds. Once dissociated, however, free sulfhydryl groups randomly re-associate with other sulfhydryl groups to form new disulfide bond between polypeptides. Thiyl radicals can also randomly re-associate with other thiyl radicals to form new disulfide bonds or thiyl radicals may react with other amino acids to create new forms of cross-linking between polypeptides. Because one polypeptide contains multiple thiol groups, random cross-linking between polypeptide leads to formation of an “aggregated” polypeptide network, which is relatively brittle and leads to a loss of flow properties.
As such, a need currently exists for a solventless approach/method to create a composition that comprises the environmentally friendly benefits of an active essential oil while providing a stable composition that is able to provide continuous functional benefits to users.